Question

假设我们有一个像以下的mysql表：

id   parent_id   date_created   previous_status   next_status

此表显示parent_id在date_created日期面临状态更改。如何创建视图或简单查询以显示每个时间段上每个父项的状态。例如：

id   parent_id   date_created   previous_status   next_status
1    1           2015-10-11     new               old   
2    1           2015-10-12     old               med
3    1           2015-10-13     med               new   
...
...
...

结果

parent_id  status from_date   to_date
1          new    null        2015-10-11
1          old    2015-10-11  2015-10-12
1          med    2015-10-12  2015-10-13
1          new    2015-10-13  null
...
...
...

这是一个示例数据库表：Sample audit table

Answer 1

获得下一个状态的一种方法是使用相关子查询。然后，查询的另一个组件获得初始状态，这表示union all：

select distinct pid, previous_status as status, null as from_date, date_created as to_date
from t
union all
select pid, next_status, date_created as from_date,
       (select date_created
        from t t2
        where t2.pid = t.pid and t2.date_created > t.date_created
        order by t2.date_created desc
        limit 1
       ) as to_date
from t;

Mysql：需要查询

1 个答案: